panic: Crash sooner with panic_handler_crash

With the feature panic_handler_crash, a panic would previously have
tried to print details (depending on other features) before calling the
RIOT panic. This feature's purpose is to shut down everything ASAP, so
instead it now also bypasses these prints, allowing the compiler to also
remove the check for whether an interrupt is active.

src/panic.rs

@@ -2,12 +2,13 @@
 fn panic(info: &::core::panic::PanicInfo) -> ! {
     use crate::thread;
 
-    let os_can_continue = crate::thread::InThread::new()
-        // Panics with IRQs off are fatal because we can't safely re-enable them
-        .map(|i| i.irq_is_enabled())
-        // Panics in ISRs are always fatal because continuing in threads would signal to the
-        // remaining system that the ISR terminated
-        .unwrap_or(false);
+    let os_can_continue = !cfg!(feature = "panic_handler_crash")
+        && crate::thread::InThread::new()
+            // Panics with IRQs off are fatal because we can't safely re-enable them
+            .map(|i| i.irq_is_enabled())
+            // Panics in ISRs are always fatal because continuing in threads would signal to the
+            // remaining system that the ISR terminated
+            .unwrap_or(false);
 
     if !os_can_continue {
         // We can't abort on stable -- but even if we could: Set a breakpoint and wait for the
@@ -49,15 +50,6 @@ fn panic(info: &::core::panic::PanicInfo) -> ! {
             let _ = stdio.write_str("!\n");
         }
 
-        if cfg!(feature = "panic_handler_crash") {
-            unsafe {
-                riot_sys::core_panic(
-                    riot_sys::core_panic_t_PANIC_GENERAL_ERROR,
-                    cstr::cstr!("RUST PANIC").as_ptr() as _,
-                )
-            }
-        }
-
         // Not trying any unwinding -- this thread is just dead, won't be re-claimed, any mutexes it
         // holds are just held indefinitely rather than throwing poison errors.
         loop {